1. Field of the Invention
The present invention relates to a method of detecting an overcoating rubber flowed in a space between a core member and a securing metal fitting of a polymer insulator having the core member, the overcoating arranged around the core member and the securing metal fitting fixed to at least one end of the core member.
2. Description of the Related Art
Generally, there is known a polymer insulator comprising a core member, overcoating arranged around the core member, and securing metal fitting fixed to at least one end of the core member. In order to keep a seal performance between the securing metal fitting and the overcoating, when such a polymer insulator is manufactured, the applicant proposed, in Japanese Patent Application No. 9-56297, a method of manufacturing the polymer insulator, in which an overcoating rubber for forming the overcoating is formed under a condition such that the securing metal fitting is set to the core member without being fixed, the securing metal fitting and the overcoating rubber are preliminarily cured, and the securing metal fitting is clamped to the core member.
In the manufacturing method mentioned above, since the securing metal fitting is simply set to the core member, in the case of forming the overcoating rubber, a V-packing is arranged in the space between the core member and the securing metal fitting, thereby preventing a flow of the overcoating rubber into the space. However, if the overcoating rubber should flow into the space between the core member and the securing metal fitting, the tensile strength of the polymer insulator is decreased. Therefore, it is necessary to detect whether the overcoating rubber has flowed into the space or not by a non-destructive manner.
As a non-destructive detection methods, there are X-rays, an ultrasonic flaw detection method, a method using acoustic emission, and so on. However, in the case of detecting whether or not the overcoating rubber which is flowed into the space between the core member and the securing metal fitting, as existent, it is not possible to detect the overcoating rubber in the space by the method of using X-ray, the ultrasonic flaw detection method and the method of using acoustic emission.